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Rates of Growth and Nutrient Uptake of Irrigated Corn as Affected by N and P Fertilization¹

ABSTRACT

Growth rates of corn and weekly uptake of major nutrients were measured in a permanent plot fertilization experiment. Bicarbonate-soluble P and NO₃-N concentration in the soil were measured four times during the growing period. High levels of nitrates in the soil (140 ppm NO₃-N) during the first month of growth suppressed dry matter production. An increase in soil phosphate concentration resulted in higher phosphate uptake and early appearance of male flowers. On the control plots, which had not received any phosphatic fertilizer for 8 years, the plants took up more phosphate than the amount estimated by the bicarbonate method. The high levels of nitrates which were found in the soil 4 weeks after seeding (140 and 70 ppm N) dropped within the fifth week to a level of 20-10 ppm N. Denitrification to gaseous compounds in the presence of living plants due to 68 mm of sprinkler-applied water is proposed as an explanation of this phenomenon.

In order to support satisfactory plant development, the soil must be able to supply at least 900 mg N and 100 mg P per week to each plant. Uptake flux values for P and N ranged between 2.6 and 22.8 x 10^-6 µg P cm^-2 sec^-1 and between 4.1 and 22.5 x 10^-5 µg N cm^-2 sec^-1, and were affected by plant age and fertilizer application.

Contribution from the Volcani Center, Agr. Res. Org., Bet Dagan, Israel. no. 1783-E. This work was supported in part by the Ford Foundation.

² Research Student and Head, respectively, Div. of Soil Chemistry and Plant Nutrition, The Volcani Center.

Received for publication March 21, 1972. Accepted for publication June 27, 1972.